Patch "powerpc: Reintroduce is_kvm_guest() as a fast-path check" has been added to the 5.10-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    powerpc: Reintroduce is_kvm_guest() as a fast-path check

to the 5.10-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     powerpc-reintroduce-is_kvm_guest-as-a-fast-path-chec.patch
and it can be found in the queue-5.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 297501a8e68937882c03890ab92ffdb1e6273a6e
Author: Srikar Dronamraju <srikar@xxxxxxxxxxxxxxxxxx>
Date:   Wed Dec 2 10:34:55 2020 +0530

    powerpc: Reintroduce is_kvm_guest() as a fast-path check
    
    [ Upstream commit a21d1becaa3f17a97b933ffa677b526afc514ec5 ]
    
    Introduce a static branch that would be set during boot if the OS
    happens to be a KVM guest. Subsequent checks to see if we are on KVM
    will rely on this static branch. This static branch would be used in
    vcpu_is_preempted() in a subsequent patch.
    
    Signed-off-by: Srikar Dronamraju <srikar@xxxxxxxxxxxxxxxxxx>
    Acked-by: Waiman Long <longman@xxxxxxxxxx>
    Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
    Link: https://lore.kernel.org/r/20201202050456.164005-4-srikar@xxxxxxxxxxxxxxxxxx
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/arch/powerpc/include/asm/kvm_guest.h b/arch/powerpc/include/asm/kvm_guest.h
index d7749ecb30d49..2fca299f7e192 100644
--- a/arch/powerpc/include/asm/kvm_guest.h
+++ b/arch/powerpc/include/asm/kvm_guest.h
@@ -7,8 +7,18 @@
 #define _ASM_POWERPC_KVM_GUEST_H_
 
 #if defined(CONFIG_PPC_PSERIES) || defined(CONFIG_KVM_GUEST)
+#include <linux/jump_label.h>
+
+DECLARE_STATIC_KEY_FALSE(kvm_guest);
+
+static inline bool is_kvm_guest(void)
+{
+	return static_branch_unlikely(&kvm_guest);
+}
+
 bool check_kvm_guest(void);
 #else
+static inline bool is_kvm_guest(void) { return false; }
 static inline bool check_kvm_guest(void) { return false; }
 #endif
 
diff --git a/arch/powerpc/include/asm/kvm_para.h b/arch/powerpc/include/asm/kvm_para.h
index 6fba06b6cfdbc..abe1b5e82547b 100644
--- a/arch/powerpc/include/asm/kvm_para.h
+++ b/arch/powerpc/include/asm/kvm_para.h
@@ -14,7 +14,7 @@
 
 static inline int kvm_para_available(void)
 {
-	return IS_ENABLED(CONFIG_KVM_GUEST) && check_kvm_guest();
+	return IS_ENABLED(CONFIG_KVM_GUEST) && is_kvm_guest();
 }
 
 static inline unsigned int kvm_arch_para_features(void)
diff --git a/arch/powerpc/kernel/firmware.c b/arch/powerpc/kernel/firmware.c
index c3140c6084c93..c9e2819b095ab 100644
--- a/arch/powerpc/kernel/firmware.c
+++ b/arch/powerpc/kernel/firmware.c
@@ -22,6 +22,7 @@ EXPORT_SYMBOL_GPL(powerpc_firmware_features);
 #endif
 
 #if defined(CONFIG_PPC_PSERIES) || defined(CONFIG_KVM_GUEST)
+DEFINE_STATIC_KEY_FALSE(kvm_guest);
 bool check_kvm_guest(void)
 {
 	struct device_node *hyper_node;
@@ -33,6 +34,7 @@ bool check_kvm_guest(void)
 	if (!of_device_is_compatible(hyper_node, "linux,kvm"))
 		return false;
 
+	static_branch_enable(&kvm_guest);
 	return true;
 }
 #endif